学步园

【题意】

t条路，问从s到e经过n条边的最小路程

【输入】

第一行n、t、s、e

接下来t行为边的长度、边的两个端点编号

【输出】

从s到e经过n条边最小路程

做flyod，本身需要枚举n次，基于快速幂思想加速

需要注意的是评测网站和noi的pascal内核都为2.0.4

递归很容易溢出

program poj3613;
type
  arr=array [0..201,0..201] of int64;
var
  n,t,i,j,k,s,e,tot,all:longint;
  dl,map,u,v,c:array [0..10001] of longint;
  dis,root,temp,p:arr;


function min (a,b:int64):int64;
begin
  if a<b then exit(a)
         else exit(b);
end;

procedure swap (var a,b:longint);
var
  i:longint;
begin
  i:=a;
  a:=b;
  b:=i;
end;

procedure qsort (s,e:longint);
var
  i,j,k:longint;
begin
  if s>=e then exit;
  i:=s;
  j:=e;
  k:=dl[(s+e) div 2];
  while i<=j do
    begin
      while dl[i]<k do inc(i);
      while dl[j]>k do dec(j);
      if i>j then break;
      swap(dl[i],dl[j]);
      inc(i);
      dec(j);
    end;
  qsort(s,j);
  qsort(i,e);
end;

begin
  fillchar(root,sizeof(root),63);
  read(n,t,s,e);
  tot:=0;
  for i:=1 to t do
    begin
      read(c[i],u[i],v[i]);
      inc(tot);
      dl[tot]:=u[i];
      inc(tot);
      dl[tot]:=v[i];
    end;
  qsort(1,tot);
  all:=1;
  k:=1;
  for i:=1 to tot do
    begin
      if dl[i]<>dl[k] then
        begin
          k:=i;
          inc(all);
        end;
      map[dl[i]]:=all;
    end;
  for i:=1 to t do
    begin
      root[map[u[i]],map[v[i]]]:=min(root[map[u[i]],map[v[i]]],c[i]);
      root[map[v[i]],map[u[i]]]:=min(root[map[v[i]],map[u[i]]],c[i]);
    end;
  tot:=1;
  while n>0 do
    begin
      dl[tot]:=n;
      n:=n div 2;
      inc(tot);
    end;
  dec(tot);
  dis:=root;
  dec(tot);
  while tot>0 do
    begin
      p:=dis;
      fillchar(temp,sizeof(temp),63);
      for i:=1 to all do
        for j:=1 to all do
          for k:=1 to all do
            temp[i,k]:=min(temp[i,k],p[i,j]+p[j,k]);
      fillchar(dis,sizeof(dis),63);
      if dl[tot] and 1 = 1 then
        for i:=1 to all do
          for j:=1 to all do
            for k:=1 to all do
              dis[i,k]:=min(dis[i,k],temp[i,j]+root[j,k])
                           else
        dis:=temp;
      dec(tot);
    end;
  s:=map[s];
  e:=map[e];
  writeln(dis[s,e]);
end.